Home → Techniques and Tips → @RISK: General Questions → Statistical Calculations in @RISK and Excel
Applies to:
@RISK, all releases
Question:
I have come across a research paper that details some problems in Excel's statistical calculations. Is there anything to this, and is @RISK affected? How can I validate the generation of random numbers in various distributions by @RISK?
Response:
The computations in all @RISK functions are done by Palisade's own program code and do not rely on Excel's numerical functions in any way. By way of example, here are some details about the two types of functions we are most often asked about:
Probability distributions (@RISK inputs): @RISK generates all its own random numbers, and these calculations are completely independent of Excel. During a simulation, @RISK produces the random numbers using Palisade program code. Excel's role in a simulation is simply to perform the computations in the Excel formulas in your worksheet.
You can easily examine the random numbers produced by @RISK. After a simulation, open the Simulation Data window (x-subscript-i icon). This will give one column per input or output variable. You can copy these numbers in the usual way and perform any desired statistical tests on them.
Summary statistics functions such as RiskMean, RiskPercentile (also called RiskPtoX), and RiskCorrel: @RISK uses Palisade program code, not Excel, to compute all of these. Again, you can verify these calculations from the raw data in the Simulation Data window.
Microsoft has acknowledged some issues with some statistical calculations in Excel 2007 and earlier, but has addressed these beginning in Excel 2010. Microsoft gives details in the paper Function Improvements in Microsoft Office Excel 2010 (PDF). But again, none of these issues affect @RISK in any version of Excel, because @RISK does its own statistical calculations for every @RISK finction and does not use Excel functions for them.
last edited: 2013-03-20